1. Field of the Invention
The present invention generally relates to electronic markers, and more particularly to a fusion pipe coupler which doubles as an electronic marker for locating the buried pipe.
2. Description of the Prior Art
Buried conduits are employed for supplying a wide variety of utilities, including pipelines for gas, water and sewage, and cables for telephone, power and television. It often becomes necessary to locate defective or damaged cables, pipes, etc., in order to repair or replace them. Conversely, it is important to know the approximate vicinity of such items in order to avoid disturbing them when digging or excavating for other purposes.
Electronic marker systems for locating buried objects are known in the art, and generally consists of two types, namely, active and passive markers. Active markers require the use of a power supply which amplifies a signal source (usually an AC signal). The signal is radiated by the underground marker and detected by a receiver unit above ground. Passive markers, in contrast, have no power supply, but rather operate in a resonant mode, responsive to a transmitted electromagnetic field.
A passive marker is basically a wire coil and capacitor surrounded in a protective envelope, which is then buried adjacent to the cable, pipe, or other object to be located. The marker is self-contained, with no external, accessible connections. Minnesota Mining & Manufacturing Co. (assignee of the present invention) markets several kinds of passive markers for different applications as part of its ScotchMark Electronic Marker System ("ScotchMark" is a registered trademark of 3M). Two such passive markers are described in U.S. Pat. Nos. 4,334,227 issued to B. Marks on June 8, 1982, and U.S. Pat. No. 4,712,094 issued to J. Bolson on Dec. 8, 1987, each of which are hereby incorporated by reference.
Passive markers are activated by radiating a signal into the ground in the area where the marker is expected to be found. The signal is emitted via an inductive coil held close to the surface. When the coil is directly over, or near, the passive marker (which is itself an inductive coil), the marker accepts energy within its bandpass and stores it, reaching a sustained amplitude during the transmission cycle. When the transmission cycle ends, the marker re-emits the signal with an exponentially decaying amplitude. A second coil within the transceiver unit acts as a receiving antenna which detects the reradiated signal, alerting the service technician with an audible tone or other indicator means. A good explanation of one such transmitter/receiver device may be found in Canadian Patent No. 993,516, which is based on a U.S. patent application, Ser. No. 523,263 (filed Nov. 13, 1974), now abandoned. A related method is disclosed in U.S. Pat. No. 4,119,908 issued to Cosman et al. on Oct. 10, 1978.
Passive markers are usually color-coded according to the particular type of utility line they mark. Specifically, gas line markers are yellow; telephone cable markers are orange; waste water tunnel markers are green; water pipe markers are blue; and power supply markers are red. Similarly, the passive marker is "coded" by tuning the coil for a specific resonant frequency. Five distinct frequencies have been designated: 83.0 kHz for gas; 101.4 kHz for telephone; 121.6 kHz for sewage; 145.7 kHz for water; and 169.8 kHz for power. In this manner, a service technician searching for, say, a gas line, cannot accidentally activate a telephone marker since his transmitter will only be sending out an 83 kHz signal, which is not within the bandwidth for a telephone marker tuned for 101.4 kHz. Of course, these frequencies have been designated by convention, and are not meant to be restrictive.
Another technical area which is relevant to the present invention, but heretofore has been unrelated to electronic markers, pertains to the coupling of two plastic pipes or conduits. When underground pipes are being laid (for sewage, gas, etc.), they must be joined in a manner which precludes leakage at the joint. Similarly, it is often necessary to repair breaks in the pipe which result in leaks. One technique for fitting the pipes together involves the use of electro-fusion couplers.
An electro-fusion coupler is a thermoplastic fitting which is designed to join the ends of two conduits. The coupler contains an electrical resistance heating element which, upon energization, raises the temperature of the thermoplastic material, causing it to flow about the conduits, thereby fusing them together. One example of an electro-fusion coupler is shown in U.S. Pat. No. 4,486,650 issued to Bridgstock et al. on Dec. 4, 1984, which is hereby incorporated by reference.
When pipe is being laid, or being repaired, it becomes convenient to situate a marker in the hole or ditch in which the pipe is laid. It would, however, be desirable and advantageous to devise an apparatus which would simultaneously fuse the pipes together and provide an electronic marker, thereby saving time and avoiding the need for two separate devices.
Accordingly, the primary object of the present invention is to provide an electronic marker for buried conduits.
Another object of the invention is to provide an electro-fusion coupler having an integral electronic marker.
Still another object of the invention is t provide such a device which may be coded for use as a marker for a particular utility.
Yet another object of the invention is to provide an apparatus which may be used with existing electro-fusion couplers in order to convert them into electronic markers.